June 9, 2003 Radio Spectrograms from the WCCRO

The following spectral views of Solar bursts from a very
active sunspot region( 375
) were made with the Windward Community College Radio Observatory radio
spectrograph. This device was developed under a grant from NASA by RF
Associates and Radio-Sky Publishing. The instrument sweeps about 10 times
per second over a specified frequency range and collects the received signal
strength in 200 channels.

The spectral view above shows two terrific groups of
flares. The peak intensities for these bursts were measured at about 3.2 million
degrees Kelvin equivalent temperature at 20.1 Mhz. In between the flares you will note
numerous horizontal lines. These are radio stations that would normally be seen
on a spectrogram of this frequency range (18 to 28 MHz) during the day. On
the right hand side are vertical bars that are the result of a calibration
signal that is injected into the receiver. The brightest red bar corresponds to
6.4 Million degrees. Most of the second burst on this spectrogram was captured
on audio at the Big Island Radio Observatory. This wav
file is about 730 kilobytes.

This second spectrogram is the result of an X2 Class X-ray
flare that occurred at 2135 UT. X-ray flares may result in a dramatic dropout in
the ionosphere's ability to reflect terrestrial radio signals. The X-rays are so
energetic that the excite the lower layers of the ionosphere into absorptive
state. It may take some time for the ionosphere to return to normal. On this
spectrogram you see a black area were only one very strong signal manages to not
be obliterated by the phenomenon. It is possible that this signal is being
seen by a different mechanism (ground wave) here in Hawaii. The two
lighter horizontal lines that cross the spectrogram are an artifact of the
receiver electronics.

In addition to attenuation of terrestrial signals, this
blackout phenomenon also stops the naturally occurring galactic background radio
noise from penetrating to the Earth's surface. Thus if you were listening
to a short-wave receiver at the time of the X-ray flare, you would not only
notice the loss of any station you were listening to, but also an eerie
loss of the static hiss that you would normally hear when you hook up the antenna.
The strip chart above shows the dramatic dropout of the background signal level
from the 20.1 MHz single frequency receivers at the WCCRO during this X-ray
flare.

Above is a chart submitted by Tom Ashcraft
showing how the phenomena was manifested at 50 MHz. Tom is a veteran observer
who notes that these drop outs are quite rare at higher frequencies.